Project Log

A project log for 1802 MemberChip Card

A retro-microcomputer in a micro-package. Learn from the ground up, just like the pioneers. Has monitor editor assembler BASIC FORTH LISP...

lee-hartLee Hart 05/13/2023 at 06:250 Comments

I've been working on this project for a few years, but only created this Project on March 28, 2023. So I'm afraid my log will have to be retroactive. Here is the history of how I arrived at this point:

1976: The August 1976 issue of Popular Electronics magazine had an article "Build the COSMAC Elf - A Low Cost Experimenter's Computer for under $80". I built one, and it worked! It taught me about computers, and started me on the path to a successful career in computers and engineering.

1980's: I furthered my education by building and using dozens of kits; test equipment, TVs, stereos, ham gear, etc. I built many brands, but Heathkits were the best. Their great designs and excellent manuals taught me how to solder, what parts look like, and how to troubleshoot and repair your own gear. College taught me the theory; but Heathkits taught me the practical side of electronics. I figured if I was going to make a kit, that was the way to do it!

2010: I retired; but still had the "itch" to do something with electronics. But computers were no fun any more. They had become appliances that were designed, built, and programmed by "someone else". They were mainly used for games, entertainment, shopping, and social media. People bought pre-assembled boards, and ran pre-written software, to do things that someone else wanted you to do.

So, I designed an updated version of my old COSMAC Elf. It ran the same software, but had greatly expanded speed, memory and features. But it was *still* simple, easy to build, and cost under $80. It was entirely built with vintage parts and through-hole technology, and fit in an Altoids tin. I called it the 1802 Membership Card. Quite a number of people wrote programs for it.

2017: There is quite an active community of 1802 enthusiasts at For April Fool's day, someone mocked up an even smaller version of my 1802 Membership Card that fit in an Altoids Smalls tin, using surface-mount parts, DIP switches for the front panel, etc. But it was a fake; it didn't actually work. Commenters pointed out that "such a thing was impossible".

Naturally, I took that as a challenge. :-) I started scheming and schematicing to see if there was any way to actually do it. I stripped the circuit to its absolute minimum, while still remaining a working computer, compatible with the existing Elf software. I wanted to stick to through-hole logic, so beginners (and old-timers like me with weak eyes and shaky hands) could build it. I figured out that it could be done with just five ICs; the CPU, RAM, ROM, address latch, and a quad NAND gate as "glue" logic.

But there wasn't room for that many ICs on an Altoids Smalls size (2.15" x 1.35") PCB. I built and debugged a prototype, but it took two stacked PCBs. It worked, but was too tall to fit in the tin.

2018: Chuck Yakym and others collaborated to put RCA's 1981 BASIC3 floating-point BASIC3 on the 1802 Membership Card. The same code ran in my MemberChip prototype, too.

2019: Aha! What if I mounted the chips on both sides of the PCB! This is often done with surface-mount parts. But with through-hole, there have to be pads for the pins on both sides. It took quite a while to figure out a layout so the top and bottom IC pads missed each other. I also had to work out an assembly order so putting parts on one side didn't block access to soldering the parts on the other side.

2020: I made my first batch of PCBs, and sent them out to various friends in the 1802 community. Since it ran the same software as my regular 1802 Membership Card, it was immediately usable with a number of programs. I got lots of good comments on fixes and improvements, and started writing a manual.

2021: Based on the feedback, I made a new batch of rev.A PCBs. The main addition was a 20-pin expansion port, plus some tweaks to make it easier to build and a better fit into the Altoids tin. Since it seemed to be more interesting to beginners than my regular 1802 Membership Card users, I started aiming the manual toward beginners. I added a "story" section, "how to solder", and some humorous examples in the hopes that it might capture people's attention and interest in a way that a plain old technical manual wouldn't.

I made the kit price low; basically just the cost of the bare board and parts. I started selling it to real customers, to get more feedback and ideas for improvements.

2/22/2022: Richard Goedeken rewrote Scott Adams classic "Adventureland" game to run on the 1802 MemberChip Card. We added it into the leftover space in the standard ROM with Chuck's monitor and BASIC3.

10/3/2022: Mike Riley developed a mini operating system for the 1802, which he called Elf-OS. It provided a way to run his many 1802 programs, including a monitor, mini assembler/editor, BASIC, FORTH, LISP, VTL2, etc. He assembled a version of it for the MemberChip Card, so I added it to the software mix.